The present disclosure relates generally to micro-electro-mechanical devices and, more specifically, to an electro-thermal scratch drive actuator.
Micro-electro-mechanical systems (MEMS) involve the integration of mechanical elements, sensors, actuators and electronics on a common silicon substrate through micro-fabrication technology. The micro-mechanical components are typically fabricated by selectively etching a silicon wafer and the conductive and insulating layers deposited thereon. Because MEMS devices are manufactured using batch fabrication techniques similar to those used for integrated circuits, unprecedented levels of functionality, reliability and sophistication can be placed on a small silicon chip at a relatively low cost.
The so-called “scratch drive” actuator is one such MEMS device, and is capable of precise, stepwise linear motion. Generally, a scratch drive actuator utilizes a flexible, conductive plate with a small bushing at one end. For example, a buried conductive layer, an insulating layer, a sacrificial layer and two conductive device layers may be successively stacked on a substrate. The bushing may be formed in the first conductive device layer, and the plate may be formed in the second conductive device layer overlying the bushing, such as by conventional photolithographic processes. The actuator may then be “released” by etching or otherwise removing the sacrificial layer, such that the bushing rests on the insulating layer and the plate rests at one end on the bushing and at the other end on the insulating layer. When a voltage is applied between the plate and the buried conductor, the plate buckles towards the substrate, pushing the bushing forward a small distance. When the voltage is removed, asymmetries in the friction between the bushing and the insulating layer result in some degree of “rectification” of motion, producing a net movement of the actuator across the substrate. The cycle can be repeated for continuous, stepwise linear motion.
However, as with all micro-electronic devices, it is desirable to reduce the complexity and overall costs of manufacturing. These goals become increasingly urgent as device scaling continues to drive device dimensions into the nano-scale realm, where feature dimensions delve well into the sub-micron range. One obstacle to achieving such scaling with a scratch drive actuator is the need for two or more conductive layers to fabricate the actuator. Because the bushing must be formed in a second conductive layer separate from the layer in which the plate is formed, limitations in sub-micron manufacturing technology impede scaling of the bushing. That is, while the plate portion of the actuator is large enough to experience some degree of scaling, the bushing is already formed at minimum attainable dimensions, such that further scaling is impractical, if not impossible. In addition, it follows from the general goal of reducing the complexity and costs of manufacturing that it is desirable to reduce the number of layers required in the manufacture of any micro-electronic device.
Moreover, the voltage required to drive the scratch drive actuator far exceeds the operating voltages of existing micro-electronic devices. For example, while most microelectronic devices are typically powered by operating voltages of 20 volts or less, conventional scratch drive actuators may require up to 150 volts for operation. Few devices incorporating MEMS and other micro-electronic devices have such elevated operating voltages available, and the end-use products incorporating the devices are seldom designed to withstand such high voltages.
Accordingly, what is needed in the art is a scratch drive actuator that addresses the problems discussed above.